Sperati did not engrave his reproductions, although several early experts, including Mueller, thought he did even as late as 1949 when they examined sets of his work. On some of his best work, he ran his reproduction through his press twice with minute offset to give "depth" to the line. Also, he was able to reproduce die sinkage by putting a piece of copper on the bed of a press and wetting the paper to conform around it.
I have a 16 page presentation on his technique here:
https://www.sperati.org/Tpages/ST.pdf